I have a 1980 CX500C with 72k miles. It "chuff"s or coughs back through the carburetors at idle speeds. I figured it was a timing issue until I looked in my downloaded shop manual that said the timing was not adjustable. Any advice?
Valves and idle speed have been adjusted. Plugs are new. I have done the cam chain adjustment procedure - no verification of the actual adjustment. The carbs have not been balanced - but the "chuff" occurs with approximately equal frequency on both sides. The exhaust is stock, but was assembled without the "gaskets" (the old ones came apart). Airbox and filter are there. I don't believe that there are any vacuum leaks. I don't believe there are any exhaust leaks before the connection to the H box.
Does the spark advance mechanism get hung up in the advanced position? When I hooked up my timing light I found myself getting sprayed with oil so I didn't really verify the setting.
That's typically a carb issue and mainly the cut off valves in each carb are what cause "backfiring". Sounds like a thorough carb cleaning, rebuilding with new cut off valves and a carb synch afterwards are in order.
The timing on these bikes is for all intents and purposes fixed and never needs adjusting.On the CDI versions the Advance and Retard is taken care of by,"Hall Effect" set of small pulsar coils in rear case of the engine.The main timing by Larger Pulsars that are located around the Starter Flywheel.In the TAI engines the Advance and Retard is taken care of by a mechanical unit in the same rear case position.
Your coughing still could be an air-leak or carb related including faulty Float heights.
Hmm, while these normally only cause issues at higher speeds, they aren't hard to check. When I was having my issues I was told numerous times to check them...ended up putting it off in favor of "easier" things, then did 'em all in a short amount of time, and was running perfectly.
Look at your plugs, check the gap. Check the spark plug caps (actually, spark plug caps affected my idle a lot!). They aren't hard to take apart and clean, and guides can be found on here. If they were dirty, once they're cleaned it'll be a world of difference. Or just buy new ones. Since you mentioned having a timing light, hook one up to one or the other coil and see if the light goes out when it coughs. It did on my bike, which confirmed that it was ignition. If the light doesn't go off, it's carburetor related.
Also to fix my issue, I put on an ignitech (well worth the cash) and tecoparts coils (super duper cheap!).
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